A general framework of an overlay network is to implement an application carried on the network and to separate from other network traffic without large-scale modification of the infrastructure network; besides the overlay network is mainly an IP-based infrastructure network technology. The basic principle of the overlay technology is enabling the virtual machines to communicate in a tunnel through a tunnel encapsulation technology.
The Software Defined Network (SDN) technology is novel network communication architecture. The SDN technology realizes collective control and distributive forwarding of network devices. In the concept of the SDN technology, the network function is divided into two parts: controlling device and data channel, which interact therebetween through a secure channel. The controlling device may perform a collective management of the network devices under its control, uniformly arrange the network behaviors, and then prescribe the forwarding behaviors of data paths. The SDN technology greatly enhances the controllability and flexibility of network management.